The present invention relates to a power focus device for a camera, and more particularly, to a power focus device for focusing a lens by means of an electric motor drive responsive to a spring biased lever control. The invention is especially useful in underwater camera applications.
Power locus mechanisms having a lens focused by a motor drive mechanism have been proposed employing a variety of control schemes.
Japanese Laid-open Patent Publication No. 63-177118 discloses a power focus mechanism employing a rotating control dial. Rotating the control dial generates pulse signals, whose frequency and count are produced in accordance with rotation of the dial. The pulse signals are used to control an electric motor for adjustment of a lens. The direction and speed of adjustment of the lens is controlled by the direction and the speed of rotation of the dial. Such a mechanism necessitates placement of the dial on the outside of the camera so that it may be operated manually. The need to have an exposed rotatable dial makes this approach unsuitable for applications in an underwater camera because during operation, it is necessary to rotate the dial many times in order to achieve a proper focus. Such manual operation results in user fatigue and detracts from the utility of the control mechanism.
Japanese Laid-open Patent Publication No. 59-64816 also discloses a power focus device using first and second button switches. The lens is focused in a first direction while the first button is depressed and in a second direction while the second button is depressed. Such a control mechanism lends itself to sealing by pliable switch covers. However, such a mechanism does not permit real-time operation of the camera lens. The mechanism has only two switches corresponding to each of the two directions. Each switch drives the lens at a constant speed in its given direction. This speed may be either too slow for large focus adjustments or too fast for fine focus adjustments. Providing dual speeds in each direction offers greater flexibility but complicates the operation of such a control. A user operating a dual speed control must first select one speed to effect a large change in focus and then shift to a slower speed to effect a fine focus adjustment.
Thus, there exists a need for a power focus mechanism that can be easily sealed for applications involving underwater cameras while allowing variable speed operation of the lens focusing mechanism. Furthermore, such a mechanism must provide for ease of manual operation so that focusing may be readily accomplished without subjecting the user to fatigue.